The structure of CoBLM bound to d(CCAGTACTGG) has been solved (J. Am. Chem. Soc. 1996, 118, 1281-1294). Binding results form partial intercalation of the bithiazole tail 8' to the sight of DNA cleavage. The hosts for sequence selectivity of cleavage, at G 3' to pyrimidine has been identified to involve hydrogen bonding interaction between the N3 and 2 amino group of G and the amino group and N3 of the pyrimidine of CoBLM. The hydrogen of the hydroperoxide of CoBLM has been identified and modeling reveals it is located 2.5 from the hydrogen atom of the DNA that is abstracted. We have obtained data on phleomycin and deglyco BLMs (green and brown forms) bound to this sequence. We have also acquired data for CoBLM green and brown bound to a "hot spot" for double-stranded cleavage. The mode of binding and basis of recognition is very similar to that observed with d(CCAGGCCTGG), although we are still returning the model. We will look at a variety of deglyco mutant BLMs, provided by Boger's laboratory at Scripps, to try to understand how a single molecule of BLM can effect the double-stranded breaks.